His failure to receive tenure caused controversy, as it was widely believed to be due to his activism and Socialist leanings.[2][3] It is alleged that he was a Stalinist sympathizer. He was blacklisted by the HUAC in the 1950s.

In the late 1930s he (along with D.N. Pritt, Upton Sinclair, Bertolt Brecht, Lion Feuchtwanger and others) defended the Moscow Trials from critics. He claimed that, as a former Chairman of the Legislative Commission on Jails in the State of Connecticut, he had seen hundreds of criminals bluntly confess based on overwhelming evidence against them, and compared this with the reactions of the Moscow Trials defendants. He did, however, note that "there is a lot of false testimony in a trial of this kind."[4]

He founded the American group "Promoting Enduring Peace", issuing reprints of articles in pamphlet form that opposed militarism in the mid-1940s and formally forming the organization in 1952. As the first director of the organisation he organized many trips to the USSR for purposes of advocacy during the Cold War. The Gandhi Peace Award was first proposed by him, on March 13, 1959, and presented to the first recipient, Eleanor Roosevelt, the following year.